Vertical deflection circuit

ABSTRACT

A saw-tooth wave signal is supplied to the non-inverting input terminal of a first power amplifier constituting a first negative feedback amplifier. The output terminal of the first power amplifier is connected to one terminal of a deflection coil. A signal output from the other terminal of the deflection coil is supplied to the inverting input terminal of the first power amplifier. The other terminal of the deflection coil is connected, through a resistor, to the output terminal of a second power amplifier constituting a second negative feedback amplifier. The output terminal of the second power amplifier is connected to the inverting input terminal of the second power amplifier. The DC voltage appearing at the output terminal of the second power amplifier in the non-signal state is set to be equal to that of the first negative feedback amplifier. A circuit means is provided between the non-inverting input terminal of the second power amplifier and the first non-inverting input terminal for operating the second power amplifier in the phase opposite to that of the first power amplifier.

TECHNICAL FIELD

The present invention relates to a low-frequency power circuit and, moreparticularly, to a vertical deflection circuit of a television receiver.

BACKGROUND ART

FIG. 4 shows a conventional SEPP (Single Ended Push-Pull) type verticaldeflection circuit comprising a single power source.

An input terminal 1 for receiving a saw-tooth wave signal is connectedto the non-inverting input terminal of a power amplifier 2. The outputterminal of the power amplifier 2 is connected to an output terminal 3and at the same time is grounded through resistors R1 and R2. The nodeof the resistors R1 and R2 is connected to the inverting input terminalof the power amplifier 2. A series circuit of a vertical deflection coilL, capacitors C1 and C2, and a resistor R3 is connected between theoutput terminal 3 and the node of the resistors R1 and R2. The node ofthe capacitors C1 and C2 is grounded through a resistor R4.

The resistors R1 and R2 are negative feedback resistors for determiningthe DC operating point of the output signal of the power amplifier 2.The capacitors C1 and C2 are DC-blocking capacitors. Especially, in anSEPP type vertical deflection circuit comprising a single power source,the capacitor C1 operates as a power source during a negative halfcycle. Therefore, an electrolytic capacitor having a large capacitanceof about 1,000 μF is used as the capacitor C1.

In the above arrangement, assuming that the DC voltage is Vref with nosignal being input to the input terminal 1, the potential Vo at theoutput terminal 3 is:

    Vo=Vref(R1+R2)/R2

On the other hand, during AC operation, i.e., when a saw-tooth wavesignal is input to the input terminal 1, the capacitors C1 and C2 areconductive. Thus, an AC power amplification factor Gv is approximately:

    (R3+R2)/R2

    (X.sub.c1, X.sub.c2 <<R1˜R3, R3<<R1)

where:

X_(c1) =reactance of capacitor C1

X_(c2) =reactance of capacitor C2

During an AC operation, a feedback occurs from the node A of thecapacitors C1 and C2, and accordingly, a negative feedback occurs suchthat a signal generated in the resistor R4 becomes Gv times an inputsignal. As a result, assuming that an input signal is Vin, a current

    (Vin·Gv)/R4

having a good linearity flows across the vertical deflection coil L.

However, since the conventional vertical deflection circuit is an SEPPcircuit having a single power source, the large-capacitance capacitor C1is required for DC blocking. Furthermore, since an AC saw-tooth wavesignal is supplied to the vertical deflection coil L, the resistors R1to R3, the capacitor C2, and the like are also required to determine theAC and DC operating points.

Normally, the power amplifier 2 is packaged in an integrated circuit toincrease the reliability and to lower the price. However, the capacitorsC1 and C2, the resistors R1 to R4, and the like are components that areexternally connected to the integrated circuit. When the number ofcomponents externally connected to an integrated circuit is large, thereliability is degraded and the cost increases.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a verticaldeflection circuit in which the problems associated with a conventionalvertical deflection circuit are solved and the number of componentsexternally connected to an integrated circuit is decreased to increasethe reliability and to suppress an increase in cost.

In order to solve the problems described above, the present inventionprovides a first negative feedback amplifier, having an input terminalto which a saw-tooth wave is supplied, and an output terminal connectedto one terminal of a deflection coil, a second negative feedbackamplifier, having an output terminal to which the other terminal of thedeflection coil is connected through a resistor, the output terminaloutputting a direct-current voltage which is set to be equal to that ofthe first negative feedback amplifier in a non-signal stage, and circuitmeans, provided between an input terminal of the second negativefeedback amplifier and the input terminal of the first negative feedbackamplifier, for operating the second negative feedback amplifier in aphase opposite to that of the first negative feedback amplifier.

More specifically, according to the present invention, the outputterminals of the first and second negative feedback amplifiers areconnected to each other through a series circuit of a deflection coiland a resistor. The voltages at the output terminals of the first andsecond negative feedback amplifiers in the non-signal state are setequal to each other. The second negative feedback amplifier is operatedin a phase opposite to that of the first negative feedback amplifier.Hence, a capacitor for blocking a DC output can be eliminated. DC and ACfeedback loops need not be provided. As a result, the number ofcomponents externally connected to the integrated circuit can bereduced, thereby suppressing an increase in cost.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a circuit diagram of the first embodiment of the presentinvention,

FIG. 2 is a circuit diagram of an example of a power amplifier shown inFIG. 1,

FIG. 3 is a circuit diagram of the second embodiment of the presentinvention, and

FIG. 4 is a circuit diagram of a conventional vertical deflectioncircuit.

BEST MODE OF CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described withreference to the accompanying drawings.

Referring to FIG. 1, an input terminal 11 is connected to thenon-inverting input terminal of a power amplifier 12 constituting afirst negative feedback amplifier. The power amplifier 12 is, e.g., anSEPP circuit having a single power source which is constituted by anintegrated circuit. The output terminal of the power amplifier 12 isconnected to one terminal of a vertical deflection coil 13. The otherterminal of the deflection coil 13 is grounded through a series circuitof resistors R1 and R2. The node of the resistors R1 and R2 is connectedto the inverting input terminal of the power amplifier 12.

The other terminal of the vertical deflection coil 13 is also connected,through a resistor R3 for determining a saw-tooth wave current, to theoutput terminal of a power amplifier 14 constituting a second negativefeedback amplifier. The power amplifier 14 is, e.g., an SEPP circuithaving a single power source and constituted by an integrated circuit.The output terminal of the power amplifier 14 is grounded through aseries circuit of resistors R4 and R5. The node of the resistors R4 andR5 is connected to the inverting input terminal of the power amplifier14. The non-inverting input terminal of the power amplifier 12 isconnected to the non-inverting input terminal of the power amplifier 14through an inverting amplifier 15.

FIG. 2 shows an example of the power amplifier 12 or 14.

An input differential amplifier DA is constituted by transistors Q1 toQ4. Non-inverting and inverting input terminals IN+ and IN- areconnected to the bases of the transistors Q1 and Q2, respectively. Atransistor Q5 constitutes a voltage amplification stage. The base of thetransistor Q5 is connected to the node of the collector of thetransistor Q1 and the collector of the transistor Q3. Transistors Q6 toQ10 constitute a class "B" push-pull amplifier PPA. Of the transistorsQ6 to Q10, the transistors Q6 and Q8 are power transistors whose currentpaths are series-connected between a power source Vcc and a ground GND.The node of the emitter of the transistor Q6 and the collector of thetransistor Q8 is connected to an output terminal OUT. The transistorsQ7, Q9, and Q10 are drive transistors for driving the transistors Q6 andQ8. Diodes D1 and D2, connected between the base of the transistor Q10and the output terminal OUT, and diodes D3 and D4, connected between thebase of the transistor Q7 and the base of the transistor Q9, set theidling current of transistor Q6 and Q8 in a non-signal state. Acurrent-mirror circuit CM is constituted by transistors Q11 to Q14 andresistors R1 to R5. The transistor Q11 and the resistors R1 and R5 setthe reference current. The transistor Q12 and the resistor R2 constitutethe bias current source circuit of the input differential amplifier DA.Transistors Q13 and Q14, and the resistors R3 and R4 constitute the biascurrent source circuit of the class "B" push-pull amplifier PPA.

In the above arrangement, the power amplifiers 12 and 14 operate in theopposite phases to each other through an inverting amplifier 15.Assuming that the voltage gain of the inverting amplifier 15 is one andthe potential at the input terminals of the power amplifiers 12 and 14is Vref, potentials Va and Vb at the two terminals of the resistor R3are:

    Va=(R1+R2)Vref/R2

    Vb=(R4+R5)Vref/R5

When the ratio of the resistor R1 to the resistor R2 and that of theresistor R4 to the resistor R5 are set equal to each other, thefollowing relation is obtained:

    Va=Vb

and no current flows across the output terminals of the power amplifiers12 and 14 in the non-signal state.

On the other hand, the gain with respect to an AC signal is the same asthat for the DC signal. A voltage gain Gv is:

    Gv=(R1+R2)/R2

    =(R4+R5)/R5

However, since the inverting amplifier 15 is present between the inputterminals of the power amplifiers 12 and 14, the phases of theamplifiers 12 and 14 are opposite to each other. A negative feedback isapplied on the power amplifier 12 from the node of the verticaldeflection coil 13 and the resistor R3 through the vertical reflectioncoil 13. Therefore, the gain described above is a gain between the inputterminal 11 and this node.

When a saw-tooth wave input signal Vin is supplied to the input terminal11, voltages V₁₂ and V₁₄ at the output terminals of the power amplifiers12 and 14 are:

    V.sub.12 =Gv·Vin

    V.sub.14 =-Gv·Vin=-V.sub.12

and a potential difference between the two terminals of the resistor R3is:

    V.sub.12 -V.sub.14 =2V.sub.12

As a result, saw-tooth wave current of

    2V.sub.12 /R3=2Vin·Gv/R3

flows through the vertical deflection coil 13. Hence, a current twicethat of the conventional case can be obtained.

In the above embodiment, the output terminal of the power amplifier 12is connected, through the vertical deflection coil 13 and thecurrent-determining resistor R3, to the output terminal of the poweramplifier 14 that operates in the opposite phase to that of the poweramplifier 12. As a result, no DC current flows across the outputterminals of the power amplifiers 12 and 14, and thus the verticaldeflection coil 13 and the current-determining resistors R1 and R2 canbe directly coupled to each other without using a large-capacitanceDC-blocking capacitor.

In addition, when the ratio of the resistor R1 to the resistor R2 isselected so as to obtain an optimum operating point regarding the inputDC potential, the output DC, and the output AC, in other words, toobtain a maximum amplitude, the need to provide both the AC and DCfeedback loops is eliminated, unlike in the conventional case. Hence,the number of components externally connected to the power amplifiers 12and 14 each constituted by an integrated circuit can be reduced.

FIG. 3 shows the second embodiment of the present invention. The sameportions as in FIG. 1 are denoted by the same reference numerals. Onlyportions different from those in FIG. 1 will be described.

In the first embodiment, the phase of the power amplifier 14 is set tobe opposite to that of the power amplifier 12 by using the invertingamplifier 15. In the second embodiment, the phase of a power amplifier14 is set to be opposite to that of a power amplifier 12 without usingan inverting amplifier 15.

More specifically, the non-inverting input terminal of the poweramplifier 14 is grounded, the resistor R5 of the power amplifier 14 isremoved, and the inverting input terminals of the power amplifiers 12and 14 are connected through the resistor R2 of the power amplifier 12.

In the above arrangement, the inverting input terminal of the poweramplifier 14 is grounded. Thus, the power amplifier 12 becomes anon-inverting amplifier whose gain is determined by the ratio of aresistor R1 to a resistor R2. The power amplifier 14 becomes aninverting amplifier whose gain is determined by the ratio of a resistorR4 to the resistor R2.

With this arrangement, a DC-blocking capacitor can be eliminated, as inthe first embodiment, and the number of the components can be reduced.

It is obvious that various changes and modifications can be made withoutdeparting from the spirit and scope of the invention.

INDUSTRIAL APPLICABILITY

As has been described above in detail, according to the presentinvention, a capacitor for blocking a DC output can be eliminated, andneither DC nor AC feedback loops are provided. As a result, the numberof components externally connected to an integrated circuit can bereduced, suppressing an increase in cost. Hence, the present inventionis effective in the field of television techniques and has a highapplicability.

I claim:
 1. A vertical deflection circuit comprising:a first negativefeedback amplifier having an input terminal, said input terminal beingsupplied with a saw-tooth wave, and an output terminal connected to oneterminal of a deflection coil; a second negative feedback amplifierhaving an output terminal connected to another terminal of saiddeflection coil through a resistor, said output terminal outputting adirect-current voltage that is set to be equal to that of said firstnegative feedback amplifier in a non-signal stage; and circuit means,provided between an input terminal of said second negative feedbackamplifier and said input terminal of said first negative feedbackamplifier, for operating said second negative feedback amplifier in aphase opposite to that of said first negative feedback amplifier.
 2. Avertical deflection circuit according to claim 1, wherein said circuitmeans comprises an inverting amplifier.
 3. A vertical deflection circuitaccording to claim 1, wherein said first and second negative feedbackamplifiers each comprises a single ended push-pull circuit.
 4. Avertical deflection circuit comprising:a first negative feedbackamplifier having a first inverting input terminal, a first non-invertinginput terminal, and a first output terminal, said first non-invertinginput terminal being supplied with a saw-tooth wave, said first outputterminal being connected to one terminal of a deflection coil, saiddeflection coil having another terminal negatively fed back to saidfirst inverting input terminal; a second negative feedback amplifierhaving a second inverting input terminal, a second non-inverting inputterminal, and a second output terminal connected to said anotherterminal of said deflection coil through a resistor, said second outputterminal being connected to said second inverting input terminal, andsaid second output terminal outputting a direct-current voltage that isset to be substantially equal to that of said first negative feedbackamplifier in a non-signal state; and an inverting amplifier, connectedbetween said second non-inverting input terminal of said second negativefeedback amplifier and said first non-inverting input terminal of saidfirst negative feedback amplifier, for operating said second negativefeedback amplifier in a phase opposite to that of said first negativefeedback amplifier.
 5. A vertical deflection circuit comprising:a firstnegative feedback amplifier having a first inverting input terminal, afirst non-inverting input terminal, and a first output terminal, saidfirst non-inverting input terminal being supplied with a saw-tooth wave,said first output terminal being connected to one terminal of adeflection coil, said deflection coil having another terminal negativelyfed back to said first inverting input terminal; a second negativefeedback amplifier, having a second inverting input terminal, a secondnon-inverting input terminal that is grounded, and a second outputterminal connected to said another terminal of said deflection coilthrough a resistor, said second output terminal being connected to saidsecond inverting input terminal, and said second output terminaloutputting a direct-current voltage that is set to be substantiallyequal to that of said first negative feedback amplifier in a non-signalstate; and a circuit means, connected between said second invertinginput terminal of said second negative feedback amplifier and said firstinverting input terminal of said first negative feedback amplifier, foroperating said second negative feedback amplifier in a phase opposite tothat of said first negative feedback amplifier.
 6. A vertical deflectioncircuit according to claim 5, wherein said circuit means comprises aresistor.